1. Technical Field of the Invention
This invention pertains in general to satellite-based broadcast data service. The invention pertains in particular to implementing very low power modes through synchronized sleep cycles for terminal devices that receive a satellite broadcast data service.
2. Background of the Invention
The satellite-based data broadcasting capability described in U.S. utility application Ser. No. 13/657,295, and enhanced by the invention therein, provides low-latency delivery of data that can be received by an unlimited number of users. To achieve the low-latency property, that system requires each receiver to be powered on and listening at every transmission opportunity for transmissions that may be addressed to it. This is quite different from the high-latency operation of the satellite paging service described in U.S. Pat. Nos. 5,603,079 and 5,613,194, which trades latency for the ability of receiver devices to spend a large amount of their time powered off and therefore conserving battery power. While the singly-addressed paging service has seen no subscriber growth, which is why its capacity is being repurposed to the group-addressed broadcast service, the low-power aspect of paging has significant appeal for certain broadcast users.
Of course, for any individual application the broadcast originator and its users can a priori agree upon a particular sleep cycle, such that the originator sends requests only within a window around the agreed times occurring at the agreed interval, and a user application powers on the receiver device during those same windows. However, the imprecision of this approach is such that receiver power may still be wasted due to jitter in the broadcast system; the originator lacks precise control over the transmission time of a particular broadcast data block, or burst, so some amount of slack is required to ensure successful delivery. To achieve the most precise control over delivery time, such that the receiver awakens to listen for the broadcasts in which it is interested at the precise time at which those broadcasts may be transmitted, cooperation is needed among the broadcast originator that requests a delivery, a controller that acts on these requests and schedules their actual transmission over the satellite resources, and receiver devices that must be ready for reception at the appropriate time.
Further, though the application-driven low-power mode may be sufficient for many uses, in the most general case a receiver device may be associated with multiple broadcast originators, each with its own transmission interval and corresponding receiver sleep cycle. Ideally these cycles would be mutually optimized, which again leads to methods of cooperation in which the transmission controller is involved.